From: Florian Weimer via Libc-alpha <libc-alpha@sourceware.org>
To: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Cc: libc-alpha@sourceware.org
Subject: Re: [PATCH v2 05/19] nptl: Move setxid flag out of cancelhandling
Date: Mon, 30 Aug 2021 13:27:00 +0200 [thread overview]
Message-ID: <87r1ebqikb.fsf@oldenburg.str.redhat.com> (raw)
In-Reply-To: <9282d6d3-cbb5-7975-31c9-f4088c594777@linaro.org> (Adhemerval Zanella's message of "Thu, 26 Aug 2021 13:39:53 -0300")
* Adhemerval Zanella:
> On 26/08/2021 12:21, Florian Weimer wrote:
>> * Adhemerval Zanella:
>>
>>> On 26/08/2021 08:34, Florian Weimer wrote:
>>>> * Adhemerval Zanella:
>>>>
>>>>> Now that the thread state is tracked by 'joinstate' field, there is no
>>>>> need to keep the setxid flag within the 'cancelhandling'. It simplifies
>>>>> the atomic code to set and reset it (since there is no need to handle
>>>>> the thread state concurrent update).
>>>>
>>>> Some of this functionality reimplements the tidlock.
>>>>
>>>> There is some functionality around thread creation, but I do not know if
>>>> the synchronization is entirely correct. This makes it rather difficult
>>>> to review changes.
>>>>
>>>> It's also not clear to me if we need to do anything to prevent early
>>>> setxid calls:
>>>>
>>>>> /* Don't allow setxid until cloned. */
>>>>
>>>> I suspect this should just look at the TID instead. We create the
>>>> thread with all signals blocked, so once there is a TID (and the thread
>>>> has not exited), it is safe to send the signal.
>>>
>>> I agree that we might improve the setxid code, however what I intended
>>> with this changes is to keep its semantic as-is and just decouple it
>>> from cancelhandling. I might revise it on a later patch to follow your
>>> suggestions.
>>
>> I wonder if there is a new race here:
>>
>> @@ -109,41 +100,23 @@ setxid_mark_thread (struct xid_command *cmdp, struct pthread *t)
>> /* Don't let the thread exit before the setxid handler runs. */
>> t->setxid_futex = 0;
>>
>> + /* If thread is exiting right now, ignore it. */
>> + if (atomic_load_acquire (&t->joinstate) == THREAD_STATE_EXITING)
>> + return;
>>
>> + /* Release the futex if there is no other setxid in progress. */
>> + if (atomic_exchange_acquire (&t->setxid_flag, 1) == 0)
>> + {
>> + t->setxid_futex = 1;
>> + futex_wake (&t->setxid_futex, 1, FUTEX_PRIVATE);
>> }
>>
>> That is, if the setxid-sending thread can now wait for a futex wake that
>> never comes.
>
> Wouldn't be handled by setxid_unmark_thread, which wakes the futex
> unconditionally?
But that code only runs after the loop around signalled has concluded.
That's why I'm worried.
Thanks,
Florian
next prev parent reply other threads:[~2021-08-30 11:27 UTC|newest]
Thread overview: 68+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-23 19:50 [PATCH v2 00/19] Fix various NPTL synchronization issues Adhemerval Zanella via Libc-alpha
2021-08-23 19:50 ` [PATCH v2 01/19] nptl: Fix tst-cancel7 and tst-cancelx7 race condition (BZ #14232) Adhemerval Zanella via Libc-alpha
2021-08-26 9:33 ` Florian Weimer via Libc-alpha
2021-08-23 19:50 ` [PATCH v2 02/19] nptl: Set cancellation type and state on pthread_exit Adhemerval Zanella via Libc-alpha
2021-08-26 9:38 ` Florian Weimer via Libc-alpha
2021-08-26 9:42 ` Florian Weimer via Libc-alpha
2021-08-26 11:56 ` Adhemerval Zanella via Libc-alpha
2021-08-26 11:52 ` Adhemerval Zanella via Libc-alpha
2021-08-26 12:08 ` Florian Weimer via Libc-alpha
2021-08-23 19:50 ` [PATCH v2 03/19] nptl: Handle robust PI mutexes for !__ASSUME_SET_ROBUST_LIST Adhemerval Zanella via Libc-alpha
2021-08-26 9:42 ` Florian Weimer via Libc-alpha
2021-08-26 12:14 ` Adhemerval Zanella via Libc-alpha
2021-08-23 19:50 ` [PATCH v2 04/19] nptl: Do not use pthread set_tid_address as state synchronization (BZ #19951) Adhemerval Zanella via Libc-alpha
2021-08-26 10:41 ` Florian Weimer via Libc-alpha
2021-08-26 14:58 ` Adhemerval Zanella via Libc-alpha
2021-08-26 15:06 ` Florian Weimer via Libc-alpha
2021-08-26 16:16 ` Adhemerval Zanella via Libc-alpha
2021-08-30 10:42 ` Florian Weimer via Libc-alpha
2021-08-23 19:50 ` [PATCH v2 05/19] nptl: Move setxid flag out of cancelhandling Adhemerval Zanella via Libc-alpha
2021-08-26 11:34 ` Florian Weimer via Libc-alpha
2021-08-26 15:11 ` Adhemerval Zanella via Libc-alpha
2021-08-26 15:21 ` Florian Weimer via Libc-alpha
2021-08-26 16:39 ` Adhemerval Zanella via Libc-alpha
2021-08-30 11:27 ` Florian Weimer via Libc-alpha [this message]
2021-08-23 19:50 ` [PATCH v2 06/19] nptl: Replace struct thread cancelhandling field Adhemerval Zanella via Libc-alpha
2021-08-26 14:34 ` Florian Weimer via Libc-alpha
2021-08-26 16:48 ` Adhemerval Zanella via Libc-alpha
2021-08-30 10:36 ` Florian Weimer via Libc-alpha
2021-08-23 19:50 ` [PATCH v2 07/19] support: Add support_wait_for_thread_exit Adhemerval Zanella via Libc-alpha
2021-08-26 9:31 ` Florian Weimer via Libc-alpha
2021-08-26 16:49 ` Adhemerval Zanella via Libc-alpha
2021-08-30 11:46 ` Florian Weimer via Libc-alpha
2021-08-23 19:50 ` [PATCH v2 08/19] nptl: pthread_kill, pthread_cancel should fail after exit (bug 19193) Adhemerval Zanella via Libc-alpha
2021-08-26 10:03 ` Florian Weimer via Libc-alpha
2021-08-26 16:49 ` Adhemerval Zanella via Libc-alpha
2021-08-23 19:50 ` [PATCH v2 09/19] nptl: Fix race between pthread_kill and thread exit (bug 12889) Adhemerval Zanella via Libc-alpha
2021-08-26 14:23 ` Florian Weimer via Libc-alpha
2021-08-26 17:06 ` Adhemerval Zanella via Libc-alpha
2021-08-30 9:25 ` Florian Weimer via Libc-alpha
2021-08-23 19:50 ` [PATCH v2 10/19] nptl: Use tidlock when accessing TID on pthread_getaffinity_np Adhemerval Zanella via Libc-alpha
2021-08-26 14:24 ` Florian Weimer via Libc-alpha
2021-08-26 17:29 ` Adhemerval Zanella via Libc-alpha
2021-08-30 9:30 ` Florian Weimer via Libc-alpha
2021-08-23 19:50 ` [PATCH v2 11/19] nptl: Use tidlock when accessing TID on pthread_setaffinity Adhemerval Zanella via Libc-alpha
2021-08-26 14:25 ` Florian Weimer via Libc-alpha
2021-08-26 17:31 ` Adhemerval Zanella via Libc-alpha
2021-08-23 19:50 ` [PATCH v2 12/19] nptl: Use tidlock when accessing TID on pthread_getcpuclockid Adhemerval Zanella via Libc-alpha
2021-08-26 14:27 ` Florian Weimer via Libc-alpha
2021-08-26 17:41 ` Adhemerval Zanella via Libc-alpha
2021-08-30 9:34 ` Florian Weimer via Libc-alpha
2021-08-23 19:50 ` [PATCH v2 13/19] nptl: Use tidlock when accessing TID on pthread_getschedparam Adhemerval Zanella via Libc-alpha
2021-08-26 15:00 ` Florian Weimer via Libc-alpha
2021-08-23 19:50 ` [PATCH v2 14/19] nptl: Use tidlock when accessing TID on pthread_setschedparam Adhemerval Zanella via Libc-alpha
2021-08-26 14:35 ` Florian Weimer via Libc-alpha
2021-08-23 19:50 ` [PATCH v2 15/19] nptl: Use tidlock when accessing TID on pthread_getname_np Adhemerval Zanella via Libc-alpha
2021-08-26 14:38 ` Florian Weimer via Libc-alpha
2021-08-26 17:45 ` Adhemerval Zanella via Libc-alpha
2021-08-30 9:37 ` Florian Weimer via Libc-alpha
2021-08-23 19:50 ` [PATCH v2 16/19] nptl: Use tidlock when accessing TID on pthread_setname_np Adhemerval Zanella via Libc-alpha
2021-08-23 19:50 ` [PATCH v2 17/19] nptl: Use tidlock when accessing TID on pthread_sigqueue Adhemerval Zanella via Libc-alpha
2021-08-26 14:43 ` Florian Weimer via Libc-alpha
2021-08-26 17:49 ` Adhemerval Zanella via Libc-alpha
2021-08-30 9:26 ` Florian Weimer via Libc-alpha
2021-08-23 19:50 ` [PATCH v2 18/19] nptl: Use tidlock when accessing TID on pthread_setschedprio Adhemerval Zanella via Libc-alpha
2021-08-23 19:50 ` [PATCH v2 19/19] nptl: Remove INVALID_TD_P Adhemerval Zanella via Libc-alpha
2021-08-26 9:30 ` Florian Weimer via Libc-alpha
2021-08-26 14:47 ` [PATCH v2 00/19] Fix various NPTL synchronization issues Florian Weimer via Libc-alpha
2021-08-26 18:19 ` Adhemerval Zanella via Libc-alpha
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